rpi-eeprom-update: scan only /dev/mmcblk0p1 in findBootFS

[sairon]

Make findBootFS check faster by scanning only the device that it looks for. Running blkid without argument can block for several seconds if any of the devices is busy and if the device doesn't exist, the command returns immediately. The regular expression already constrains the output to match only one device, so scanning all superblocks is wasteful.

[sairon]

Note that this change is a result of adapting rpi-eeprom-update in Home Assitant OS, so I'm not sure if RPi OS is concerned by it, nevertheless I think is a reasonable optimization.

Here's some profiling results from HA OS:

# time blkid /dev/mmcblk0p1
Command exited with non-zero status 2
real    0m 0.00s
user    0m 0.00s
sys     0m 0.00s
# time blkid /dev/sda1
/dev/sda1: SEC_TYPE="msdos" LABEL_FATBOOT="hassos-boot" LABEL="hassos-boot" UUID="099B-856A" BLOCK_SIZE="512" TYPE="vfat" PARTLABEL="hassos-boot" PARTUUID="b3dd0952-733c-4c88-8cba-cab9b8b4377f"
real    0m 2.06s
user    0m 0.00s
sys     0m 0.00s
# time blkid
/dev/sda1: SEC_TYPE="msdos" LABEL_FATBOOT="hassos-boot" LABEL="hassos-boot" UUID="099B-856A" BLOCK_SIZE="512" TYPE="vfat" PARTLABEL="hassos-boot" PARTUUID="b3dd0952-733c-4c88-8cba-cab9b8b4377f"
/dev/zram1: LABEL="hassos-var" UUID="533795f9-21b1-44f0-bc2d-feb44afed1bb" BLOCK_SIZE="4096" TYPE="ext4"
/dev/zram2: LABEL="hassos-tmp" UUID="54529d52-0bee-4eca-87a5-001602570717" BLOCK_SIZE="4096" TYPE="ext4"
/dev/sda4: PARTLABEL="hassos-kernel1" PARTUUID="fc02a4f0-5350-406f-93a2-56cbed636b5f"
/dev/sda2: BLOCK_SIZE="131072" TYPE="squashfs" PARTLABEL="hassos-kernel0" PARTUUID="26700fc6-b0bc-4ccf-9837-ea1a4cba3e65"
/dev/sda7: LABEL="hassos-overlay" UUID="788cf76a-5d2a-4737-8c32-90510b74869e" BLOCK_SIZE="1024" TYPE="ext4" PARTLABEL="hassos-overlay" PARTUUID="f1326040-5236-40eb-b683-aaa100a9afcf"
/dev/sda5: PARTLABEL="hassos-system1" PARTUUID="a3ec664e-32ce-4665-95ea-7ae90ce9aa20"
/dev/sda3: UUID="fa626bec-d47b-4f3a-97ef-b0636a9b3915" BLOCK_SIZE="4096" TYPE="erofs" PARTLABEL="hassos-system0" PARTUUID="8d3d53e3-6d49-4c38-8349-aff6859e82fd"
/dev/sda8: LABEL="hassos-data" UUID="f03be0cd-9635-4491-b886-4b545c34d6f1" BLOCK_SIZE="4096" TYPE="ext4" PARTLABEL="hassos-data" PARTUUID="a52a4597-fa3a-4851-aefd-2fbe9f849079"
/dev/sda6: PARTLABEL="hassos-bootstate" PARTUUID="33236519-7f32-4dff-8002-3390b62c309d"
real    0m 38.62s
user    0m 0.00s
sys     0m 0.16s
#

[timg236]

Looks ok

[timg236]

@sairon FYI, this draft PR might be of interest to HA OS. It's designed to reduce the risk of accidental bootloader downgrades to versions which don't support the hardware (e.g. different SDRAM / flash / PMIC etc)

https://github.com/raspberrypi/rpi-eeprom/pull/844/changes